1. Field of the Invention
The embodiments disclosed herein are related to a controlling apparatus for controlling an engine mounted on a vehicle.
2. Description of the Related Art
Conventionally, a controlling apparatus for controlling an idle speed of an engine mounted on a vehicle is known. In the controlling apparatus, idle control for controlling the engine speed to a target engine speed is carried out in the case where the driving state of the vehicle satisfies a predetermined idle condition. As a particular example of the idle control, feedback control of an intake air amount to the engine, an ignition timing of each cylinder of the engine and so forth are available.
Incidentally, the engine speed fluctuates in response to the load acting upon the engine. Since the idle speed is set lower than the engine speed upon normal vehicle running, if an external load acts upon the engine during idle operation, then there is the possibility that the engine may stall. From such a point of view as just described, various techniques regarding control for securing idle stability have been developed.
For example, in Japanese Patent Laid-Open No. 61-96146, idle control for a vehicle including a power steering apparatus is disclosed. According to the idle control, a power steering correction term is calculated based on an angular speed ω of a steering angle, and the intake air amount is controlled based on the calculated value. By such a configuration as just described, fluctuation of the idle speed can be prevented.
However, the external load acting upon the engine upon the steering operation fluctuates in response to the angle of the steering wheel. For example, in a hydraulic power steering apparatus for driving a steering pump to assist the steering force, the magnitude of a load generated in a state in which the steering wheel is fully operated is higher than that at a steering position at or around the neutral position of the steering wheel. Also in an electrically-operated power steering apparatus, the load acting upon the engine increases as the steering angle increases. Accordingly, in such conventional idle control which is based on the angular speed ω as disclosed in Japanese Patent Laid-Open No. 61-96146, there is a subject that it is difficult to calculate an accurate value of the external load and the idle stability is liable to degrade.
Also it is imaginable to set, regarding the idle stability, the idle speed rather high in advance to avoid stall of the engine. For example, in the technique disclosed in Japanese Patent Laid-Open No. 61-96146, the intake air amount is controlled rather great in advance. However, in this instance, the engine rotates excessively irrespective of the magnitude of the external load, and energy loss increases to degrade the fuel cost.